Comparison of methods for determining budburst date in grapevine

Methods for determining budburst date in grapevine are poorly documented. Budburst date defined from cumulative shoots burst (or arising) and cumulative buds burst (expressed as % of total) were compared using different cultivars, pruning systems and irrigation treatments and assessed at the plant, bearer and individual bud level. The study was conducted at three sites within an Australian vineyard over two years on mechanical pruned Chardonnay and Cabernet-Sauvignon; mechanical, spur and minimally pruned Shiraz; and control, regulated and prolonged deficit irrigated Cabernet-Sauvignon. Budburst defined as ‘50 % of total shoots burst’ was more reliable than ‘50 % of buds burst’ for determining budburst date when final % budburst was low, as observed under lighter (mechanical or minimal) pruning for Shiraz. Differences in final % budburst between pruning systems and deficit irrigation treatments were related mainly to the distribution (%) of bearers according to size (based on node or bud numbers) and their specific budburst percentage at each node position. The timing of budburst based on ‘50 % of total shoots burst’ was dependent on a unique set of parameters for each cultivar, regardless of pruning treatments and irrigation levels. The new knowledge gained in this study about the impact of pruning system and irrigation treatment on % budburst and timing may be useful for adapting phenological models to Australian vineyards.